The present invention relates to a control apparatus and a control method for an internal combustion engine, and more particularly to a control apparatus and a control method for an internal combustion engine, the control apparatus including means for controlling an air/fuel ratio and means for determining deterioration of the catalyst based on an oxygen storage volume of the catalyst.
Among control units for controlling the air/fuel ratio of an internal combustion engine, there is a type that computes an absolute volume of oxygen stored in a catalyst based on output of an air/fuel ratio sensor (an O2 sensor or a linear air/fuel ratio sensor) for detecting exhaust components installed on the upstream side of the catalyst in the exhaust passage of the engine and also based on output of an airflow sensor for measuring a volume of air drawn into the combustion chamber of the engine, and that controls the air/fuel ratio based on an estimated oxygen storage volume of the catalyst (e.g., JP-A-2002-81339).
As a detector for detecting a degree of deterioration of the catalyst, there is a type that estimates an absolute volume of oxygen stored in the catalyst based on output of an air/fuel ratio sensor mounted on the downstream side of the catalyst, and detects deterioration of the catalyst based on this estimated value (e.g., JP-A-5-133264). In addition, there has been proposed a diagnosis unit for diagnosing deterioration of the air/fuel ratio sensor, which is designed to improve the robustness (anti-deterioration properties) of the air/fuel ratio sensor on the upstream side of the catalyst (e.g., JP-A-8-220051).